This invention relates to multifunctional/antioxidant/antiwear-EP additives and to compositions comprising lubricants, greases and other solid lubricants thereof containing a minor amount of an ashless organic hydrogen phosphonate derived from a dithiocarbamate.
The metal surfaces of machinery or engines operate under heavy or normal loads wherein the metal is under friction, even when being lubricated. Thus, there is always metal wear which in some cases can be excessive. It is clear that lubricants used to protect the metal surfaces do not completely prevent wear at the points of metal to metal contact. Consequently, the performance of the machine or engine will suffer, and in aggravated cases the machine or engine may be become completely inoperative from the wear caused by the friction and the load.
There have been many attempts to devise additive systems to improve the extreme pressure/load carrying properties of a lubricant. The non-metallic derivatives of the present invention provide lubricating oil compositions with enhanced antioxidant/antiwear and extreme pressure/load carrying characteristics and are believed to be capable of overcoming some of the aforementioned deficiencies of prior art additives.
Lubricants, such as lubricating oils and greases, are subject to oxidative deterioration at elevated temperatures or upon prolonged exposure to the elements. Such deterioration is evidenced, in many instances, by an increase in both acidity and viscosity, and when the deterioration is severe enough, it can cause metal parts to corrode. Additionally, severe oxidation leads to a loss of lubrication properties, and in especially severe cases this may cause complete breakdown of the device being lubricated. Many additives have been tried, however, many of them are only marginally effective except at high concentrations. Improved antioxidants are clearly needed.
Antioxidants or oxidation inhibitors are used to minimize the effects of oil deterioration that occur when, for example, hot oil is contacted with air. The degree and rate of oxidation will depend on temperature, air and oil flow rates and, of particular importance, on the presence of metals that may catalytically promote oxidation. Antioxidants generally function by prevention of chain peroxide reaction and/or metal catalyst deactivation. They prevent the formation of acid sludges, darkening of the oil and increases in viscosity due to the formation of polymeric materials.
Water (moisture) is another critical problem. In spite of even extraordinary precautionary efforts water is found as a film or in minute droplets in vessels containing various hydrocarbon distillates. This brings about ideal conditions for corrosion and damage of metal surfaces of the vessels and the materials contained therein. Also in the lubrication of internal combustion engines, for example, quantities of water are often present as a separate phase within the lubricating system. Another serious problem as previously mentioned in respect to metallic surfaces in contact with adjacent metallic surfaces is the surface wear caused by the contact of such surfaces. One material capable of simultaneously coping with such problems effectively is highly desirable.
The use of metal dithiocarbamates (such as zinc, nickel, or lead dialkyl dithiocarbamates) are known as effective antioxidants and antiozonants for many rubbers and polymers in various kinds of applications, such as styrene butadiene rubber and acrylonitrile butadiene rubber.
The use of non-metallic (ashless) dithiocarbamates, such as 4,4'-methylene bis(dibutyl dithiocarbamate), has been well known for their antioxidant and extreme pressure properties in lubricant applications.
The use of organic, dialkyl or diaryl hydrogen phosphonates, such as dibutyl hydrogen phosphonate and dioleyl hydrogen phosphonate, has been widely reported as having beneficial antiwear and extreme pressure properties.
It has now been found that the use of dithiocarbamate-derived organic hydrogen phosphonates provides exceptional antioxidant and antiwear/EP activity with potential high temperature stabilizing and metal passivating properties.